1. Field of the Invention
This invention relates generally to sunscreen and tanning lotions. More particularly, this invention relates to a lotion that is applied to the skin and which contains photochromic compounds that react upon exposure to ultraviolet radiation, e.g. sunlight, to produce a color change, simulating a suntan, and which also react to provide protection against ultraviolet radiation, thus producing a synergistic effect.
2. Prior Art
Because of work-related and/or recreational activities, most people spend at least some portion of their lives outdoors and are therefore exposed to sunlight. exposure to sunlight, and more specifically, exposure to the UV rays in sunlight, creates free radicals that ultimately break down the protein network in the skin. In mild cases this leads to photo-aging and wrinkling of the skin, and in more severe cases can lead to the growth of cancerous cells (melanoma).
In spite of these hazards, which are generally known, many people seek exposure to sunlight, or to the UV lamps in a tanning salon, in order to obtain a tan. In fact, many people use the services of a tanning salon so that they can obtain a tan prior to visiting a public pool or beach.
Whether they are going to be exposed to natural sunlight or to the UV lamps in a tanning salon, most people apply some type of skin protection, e.g., tanning lotions and/or sunscreens, in order to avoid becoming burned and to minimize the risks associated with exposure to UV radiation.
Sunscreens are formulated with UV inhibitors or absorbers to block or reduce the amount of UV rays reaching the skin, thereby reducing or eliminating the potential damage caused by exposure to UV radiation. Approved sunscreen actives include aminobenzenic acid, avobenzone, cinoxate, dioxybenzone, homosalate, menthyl anthranilate, octocrylene, octyl methoxycinnamate, octyl salicylate, oxybenzone, padimate, phenylbenzinadazole sulfonic acid, sulisbenzone, trolamine salicylate and zinc oxide. Two or more of these active ingredients may be combined with other materials to produce a cream, lotion or spray lotion with an appropriate sun protection factor (SPF) and broad spectrum sun protection and that is chemical- and photo-stable is water resistant and has reduced skin penetration. Suspoemulsions can also be used to insure that the most protection is obtained from selected sunscreen combinations, e.g., to combine amphophilic microfine titanium dioxide with organic sunscreens using relatively small amounts of sunscreen actives.
Persons venturing to the pool or beach for at least the first few times following a season indoors may be self-conscious about their lack of a tan, and are therefore anxious to obtain a tan as quickly as possible. However, if these persons are applying a sunscreen as protection from the harmful effects of UV radiation, they are also delaying the tanning process since the very benefits conferred by the sunscreens also tend to impede tanning of the skin. Consequently, many people forego the benefits of a sunscreen in favor of more quickly obtaining a tan.
At least partially in response to these problems, the cosmetics industry has developed products that alter the tone or color of the skin in order to produce an artificial tan. However, these artificial tanning products do not provide the protection imparted by a sunscreen, nor do the artificial tans obtained by their use appear the same as a tan obtained from exposure to sunlight or to the UV lamps in a tanning salon. Further, use of these products may lead to a false sense of security since the person""s skin remains unprotected against the harmful effects of UV radiation even though it appears tan, and the person""s skin can become burned if exposed for even a short period of time to sunlight or to the UV lamps in a tanning salon.
Accordingly, there is need for a tanning lotion and sunscreen that effectively protects the skin from the harmful effects of UV radiation, but which at the same time confers the appearance of a tan as soon as exposed to UV radiation, whereby a person can cosmetically appear as though already tanned while seeking a tan, and at the same time be protected against the harmful effects of exposure to UV radiation.
The invention provides a tanning lotion and sunscreen that effectively protects the skin from the harmful effects of UV radiation, but which at the same time confers the appearance of a tan as soon as exposed to UV radiation, whereby a person can cosmetically appear as though already tanned at the same time he or she is seeking a tan.
More particularly, the invention comprises a tanning lotion or sunscreen formulation having photochromic compounds that change color upon exposure to sunlight or other sources of ultraviolet radiation (UV) to create the appearance of a tanned skin. As part of the color changing process, the molecules of the photochromic compounds open up and provide a UV blocking effect. Thus, the photochromic compounds produce a synergistic effect in the tanning lotion of the invention. That is, the lotion reacts to UV radiation to change color, and also blocks UV radiation.
The photochromic compounds may be mixed in a carrier that can be added to the normal formulation of a skin lotion. If desired, an additional UV absorber can be provided in these formulations which also may include a pigment and an emollient. In order to get the most protection out of sunscreen combinations, the formulator can use suspoemulsions to combine amphiphilic microfine titanium dioxide with organic sunscreens using relatively small amounts of sunscreen actives. One or more sunscreen actives may be selected from the following: aminobenzenic acid, avobenzone, cinoxate, dioxybenzone, homosalate, menthyl anthronilate, octocrylene, octyl methoxycinnamate, octyl salicylate, oxybenzone, padimate, phenylbenzinadazole sulfonic acid, sulisbenzone, trolamine salicylate and zinc oxide. This technology makes it possible to develop creams, lotions and spray lotions with high SPF and broad-spectrum sun protection.
To make suspoemulsions, titanium dioxide is added to the oil phase. Emolients with medium polarity are preferred so that a desired viscosity can be maintained in a narrow range over a wide concentration range of titanium dioxide. The formulation can be thickened by using Polyquat 37 and propylene glycol.
Examples of suitable photochromic compounds are described in U.S. Pat. Nos. 5,581,090 and 5,730,961, the disclosures of which are incorporated in full herein by reference. As noted in the ""090 and ""961 patents, photochromic substances are known in the art for their utilization in optics as storage media or as a means to detect UV, such as, e.g., the photochromic ultraviolet detector disclosed in the ""090 patent. Among the large family of photochromic compounds are the spiropyrans and spiroxazines groups of molecules. These molecules are known for their property of changing from clear to a variety of colors and shades. Normally appearing as colorless, these spiro-compounds undergo a photochemical transformation to intensely colored form when exposed to UV. The ""961 patent, in particular, discloses a material which remains clear until exposed to UV and which then exhibits color and thus becomes visible. The active chemical disclosed in the ""961 patent is identified as a photochromic substance such as spiropyrans or spiroxazines molecules.
U.S. Pat. No. 5,166,345 describes a photochromic compound which exhibits high color density, is stable against heat and solvent, and which has a great repeating durability in coloring-decoloring cycles. For improved performance, the photochromic compound used to impart the appearance of a tan in accordance with the present invention can be formulated using the teachings of this patent, the disclosure of which is incorporated in full herein, whereby the stability, durability and color intensity, for example, of the compound are optimized.
Further, the composition used to make the photochromic tanning lotion of the invention may be formulated so that it is operative to change color only after exposure to UV radiation for a predetermined period of time, e.g., a few minutes. Preferably, the photochromic compounds are selected so that the color of the tanning lotion composition changes gradually upon exposure to UV, becoming increasingly darker over a period of time when exposed to UV to thereby more accurately reflect a natural tanning process.
Additionally, the tanning lotion of the invention may be formulated so that the photochromic compounds return to colorless a predetermined time after the photochromic composition is no longer exposed to UV, whereby the natural tan obtained upon exposure to sunlight or UV lamps in a tanning salon gradually replaces the artificial tan obtained by use of the formulation of the invention.